mirror of
https://github.com/ratfactor/ziglings
synced 2024-05-04 16:46:04 +02:00
65 lines
2.6 KiB
Zig
65 lines
2.6 KiB
Zig
//
|
|
// Another useful practice for bit manipulation is setting bits as flags.
|
|
// This is especially useful when processing lists of something and storing
|
|
// the states of the entries, e.g. a list of numbers and for each prime
|
|
// number a flag is set.
|
|
//
|
|
// As an example, let's take the Pangram exercise from Exercism:
|
|
// https://exercism.org/tracks/zig/exercises/pangram
|
|
//
|
|
// A pangram is a sentence using every letter of the alphabet at least once.
|
|
// It is case insensitive, so it doesn't matter if a letter is lower-case
|
|
// or upper-case. The best known English pangram is:
|
|
//
|
|
// "The quick brown fox jumps over the lazy dog."
|
|
//
|
|
// There are several ways to select the letters that appear in the pangram
|
|
// (and it doesn't matter if they appear once or several times).
|
|
//
|
|
// For example, you could take an array of bool and set the value to 'true'
|
|
// for each letter in the order of the alphabet (a=0; b=1; etc.) found in
|
|
// the sentence. However, this is neither memory efficient nor particularly
|
|
// fast. Instead we take a simpler way, very similar in principle, we define
|
|
// a variable with at least 26 bits (e.g. u32) and also set the bit for each
|
|
// letter found at the corresponding position.
|
|
//
|
|
// Zig provides functions for this in the standard library, but we prefer to
|
|
// solve it without these extras, after all we want to learn something.
|
|
//
|
|
const std = @import("std");
|
|
const ascii = std.ascii;
|
|
const print = std.debug.print;
|
|
|
|
pub fn main() !void {
|
|
// let's check the pangram
|
|
print("Is this a pangram? {?}!\n", .{isPangram("The quick brown fox jumps over the lazy dog.")});
|
|
}
|
|
|
|
fn isPangram(str: []const u8) bool {
|
|
// first we check if the string has at least 26 characters
|
|
if (str.len < 26) return false;
|
|
|
|
// we uses a 32 bit variable of which we need 26 bits
|
|
var bits: u32 = 0;
|
|
|
|
// loop about all characters in the string
|
|
for (str) |c| {
|
|
// if the character is an alphabetical character
|
|
if (ascii.isASCII(c) and ascii.isAlphabetic(c)) {
|
|
// then we set the bit at the position
|
|
//
|
|
// to do this, we use a little trick:
|
|
// since the letters in the ASCI table start at 65
|
|
// and are numbered sequentially, we simply subtract the
|
|
// first letter (in this case the 'a') from the character
|
|
// found, and thus get the position of the desired bit
|
|
bits |= @as(u32, 1) << @truncate(ascii.toLower(c) - 'a');
|
|
}
|
|
}
|
|
// last we return the comparison if all 26 bits are set,
|
|
// and if so, we know the given string is a pangram
|
|
//
|
|
// but what do we have to compare?
|
|
return bits == 0x..???;
|
|
}
|